T-bar welded to the top, ring like the old hitching posts bolted on with tamperproof bolts. disadvantage is that it would take equipment at the pole and increae costs.
If real low-buck is the option, use pipe caps with a ring or T-bar maybe both welded to them then installed with epoxy, unless you have different meter mountings, all the ones I've seen were thread-on types. ring or T-bar would make it impossible for someone to lift a U lock over the top if they were made of a sturdy enough material, the epoxy would prevent unscrewing the cap. advantage is that all work can be done inside and the only thing you need at the pole is a 'wrench' and some epoxy
Ken.